The function $f(x)=\log _2(-x-2)-1$ is graphed below. Plot all lattice points of the inverse. Use the labeled points as your guide.

Verified Answer :

  • Determine the inverse function: \(f^{-1}(x) = -2^{x+1} - 2\).
  • Recognize that \(y\) is an integer only when \(x+1 \geq 0\), meaning \(x \geq -1\).
  • Substitute integer values of \(x \geq -1\) into the inverse function to generate lattice points \((x, y)\).
  • The lattice points on the inverse function are \(\boxed{(-1, -3), (0, -4), (1, -6), (2, -10), (3, -18), \dots}\).

Explanation

  1. Analysis of the Problem

The goal is to find all lattice points (pairs of integers \((x, y)\)) that lie on the graph of the inverse function \(f^{-1}(x)\), where the original function is \(f(x) = \log_2(-x - 2) - 1\). A lattice point \((x, y)\) is on the graph of \(f^{-1}(x)\) if and only if the point \((y, x)\) is on the graph of the original function \(f(x)\). This means we need to identify integer pairs \((x, y)\) such that \(f(y) = x\).

  1. Finding the Inverse Function

To find the inverse function \(f^{-1}(x)\), we set \(y = f(x)\) and solve for \(x\) in terms of \(y\):
\[y = \log_2(-x - 2) - 1\]
Adding \(1\) to both sides:
\[y + 1 = \log_2(-x - 2)\]
Exponentiating both sides with base \(2\):
\[2^{y+1} = -x - 2\]
Solving for \(x\):
\[x = -2^{y+1} - 2\]
Thus, the inverse function is \(f^{-1}(y) = -2^{y+1} - 2\). Since we want to express this in the standard notation \(f^{-1}(x)\), we replace \(y\) with \(x\):
\[f^{-1}(x) = -2^{x+1} - 2\]
A lattice point \((x, y)\) must satisfy \(y = -2^{x+1} - 2\), where both \(x\) and \(y\) are integers.

  1. Identifying Lattice Points

We need \(x\) and \(y = -2^{x+1} - 2\) to be integers.
For \(y\) to be an integer, \(2^{x+1}\) must be an integer. This occurs if and only if \(x + 1 \geq 0\), or \(x \geq -1\). Since \(x\) is an integer, the possible values for \(x\) are \(-1, 0, 1, 2, 3, \dots\).
Let's calculate the corresponding \(y\) values for these \(x\) values:

  • For \(x = -1\): \(y = -2^{-1+1} - 2 = -2^0 - 2 = -1 - 2 = -3\). Point: \((-1, -3)\).
  • For \(x = 0\): \(y = -2^{0+1} - 2 = -2^1 - 2 = -2 - 2 = -4\). Point: \((0, -4)\).
  • For \(x = 1\): \(y = -2^{1+1} - 2 = -2^2 - 2 = -4 - 2 = -6\). Point: \((1, -6)\).
  • For \(x = 2\): \(y = -2^{2+1} - 2 = -2^3 - 2 = -8 - 2 = -10\). Point: \((2, -10)\).
  • For \(x = 3\): \(y = -2^{3+1} - 2 = -2^4 - 2 = -16 - 2 = -18\). Point: \((3, -18)\).

The general form of these points is \((x, -2^{x+1} - 2)\) for all \(x \in \{-1, 0, 1, 2, \dots\}\).

  1. Conclusion

The lattice points on the graph of \(f^{-1}(x) = -2^{x+1} - 2\) are given by the set of ordered pairs:
\[\{(-1, -3), (0, -4), (1, -6), (2, -10), (3, -18), \dots\}\]
These can be expressed as \(\boxed{(-1, -3), (0, -4), (1, -6), (2, -10), (3, -18), \dots}\).

Examples

Lattice points are essential in digital geometry, where they represent pixelated versions of curves on a screen. If you have a logarithmic growth curve, identifying the lattice points helps computer graphic designers plot the curve accurately on a grid of pixels. For example, in a game, if a path follows a specific logarithmic function, finding the closest integer coordinates ensures the character moves along the correct pixel-based trajectory.